Company Stock Purchase Plan- worth it ?

I invest 5% of my pay into my company’s stock purchase plan which has a 1 year vesting period before I can sell the shares bought quarterly. I normally sell immediately upon the available sell date. However, the stock is down 27% this past year and more than 50% past five years . Although the past 2 or 3 quarterly purchases have been at a low price and I always think there’s no way it will go lower just for it to rise for a few days then go back down. I’ve sold the last two to three blocks of sh