Hollyoaks are guilty of doing this a lot:

Irish Lynsey - So pointless, especially after all that she had been through with Silas.
Texas
Leanne
Doug
Callum Kane - Character was just about to go to university, so why not let him leave that way? He wasn't a massive character and not that interesting.
Steph Dean - Moreso the way she died. She decided to burn herself alive instead of dying peacefully of cancer at home.
Sam & Danny Lomax - I think they had a lot more to offer as characters
Jim McGinn - They just used him as an excuse to copy Dennis Rickman's death in EE, and to pair Carmel up with Sonny.
Clare Devine

EastEnders:

Heather Trott
Pat Butcher

Pat from EastEnders, definitely. Worst decision ever made.

Danielle, Ronnie's long lost daughter

I agree.

Emmerdale:

Joe Sugden...An original character who was killed off screen in 1995...pointless.
Viv Windsor...loved her cutdowns of certain characters...

Reg Cox Eastenders he had so much to give

Yeah, Viv and Terry both perished in that fire. Seem to recall it was a very "Oh! So that's that then" moment.

I do remember the actress who played Viv saying she found it strange that Viv's funeral wasn't even in the village! It was down south where the character came from apparently.

over half of the characters that have been bumped off in Hollyoaks over the last 2 years

Viv enough said. I miss her so much. I'd love to bring her back.

Kathy. I know they wanted to bring Ben in as a character but they could have done it without killing her off. Maybe Kathy could have gone down in South Africa through being framed for financial fraud or something.

Edna Miller in Corrie was a great character back in the late 1990s/early 2000s. Was a great comical character. Shame they killed her off.

Theo from Hollyoaks back in 2002 (?) was an interesting. Was one of Hollyoaks first mass-cull through the pot climbing bus accident and also killed off Jamie too. The actor had won a place on Hollyoaks through the Hollyoaks On The Pull series and was killed off soon after. He ran the gadget shop on the show which was random as part of the village but worked

Chloe on Home and Away. Purely for shock factor, it was harrowing and also disappointing they brought back a classic character to kill her off.

In my opinion (and I'm not sure whether many would agree with me), Carl King of Emmerdale. Almost 2 years on, I still miss him!
Totally agree about Viv Windsor.

Emmerdale - Carl King & Shadrach Dingle.

EE's Kathy Beale

Emmerdale's Carl King.

I was delighted to see the back of Viv and Terry. Feeble exits though.

Tiffany Mitchell - Her pic just got shown a few weeks ago clearly Dominic would give his left arm to get her back on the show but alas it will never happen.

Cindy Beale - The possibilities for her were endless. sigh

Donna Windsor!!!

Heather Trott from EE, she was a nice kind harmless lady who had good words for people and loved having Shirley as her best mate even though she wasn't always kind to her, Dot and Patrick thought the world of Hev as well and she and Andrew made a good couple.

Daphne - My afternoons have never been the same since the 1980's.

The usual suspects for EE: Pat, Kathy, Den, Angie, Cindy etc.

EE: Pat, Angie, Kathy
ED: Viv, Terry
HO: Rhys, Sam, Danny, Jim, Clare
CS: No one really, they don't really kill people off much. And Hayley dying was the only way for her to go, there'd be outrage if she left Roy.

Mel and Sophie Burton (HO)
Jim McGinn (HO)
Doug Carter (HO)
Steph Dean(HO)

Sunita Alahan (Corrie)
Ashley Peacock (Corrie)

Danielle (EE)
Mark Fowler (EE)

Matthew King (ED)

Cameron Murry (ED) He could have killed some more people!

Killing off Tiffany Mitchell was a clever move from the writers. Her story arc was completed and her death will go down as one of the show's most memorable moments.

Killing of PAT EEs worst decision ever.

I remember that she was such a good character and was one of the only teen characters from the 90s who could make an easy return and it meant that Jesse went to prison.

It was a great storyline and defiantly created that shock factor at the time but I don't think it was right just to bring her back and then kill her off.