Leave 404 error pages as it is? Or redirecting 301?

Downsides

[silverbytes]

I use to put 301 redirections to existant pages when I took off a page to avoid 404 errors. So instead you get a 404 page if you look for something that is not online anymore, you are redirected to a related page.

Today I saw that uploading my .htaccess destroyed all my old redirections that took me a lot of work to set.

I do that because that way I don't loose traffic.
Is there any downsides besides loosing traffic, in leaving those 404 pages as they are? Or should I set all again?

[JohnRoy]

It's a traffic versus time issue

[Beagle]

Does your host provide the capability of using custom 404 pages? If so, you could set one up that would at least provide a link to your homepage for people who get a 404 error.

I don't know if it's a separate issue from traffic in general, but getting a 404 error with no explanation makes me suspicious that the site has gone belly-up and I'm likely to look for a different site. A custom 404 page lets me know the site's still around and gives me a way to get there.

[silverbytes]

I already have a custom 404 with links to main categories and home...
Anyway I wonder if it's just a problem about loosing traffic or if that affects the image of your website when gone pages are listed in search engines.

Besides, SE keep searching for those gone pages forever...