Is it safe to keep /kernel.old?

[Mark]

Dear people,

I have been applying patches over time; and when I recompile the kernel (4.9R p4), it keeps the old one around. My question is, though, is it safe to keep /kernel.old? I always keep it around, in case the new kernel has a problem. And that always seemed like a sensible policy to me. But what if one of the patches contains an exploitable bug? I run in securelevel 2, so I am not sure whether users could actually use the old kernel (once in multi-user mode). Still, I wonder if this concern is valid at all. Or whether I should perhaps get rid of the old kernel.

I appreciate your help,

- Mark