If you do not have a '.' at the end, then other things from you search path might be appended to your hostname. However, I generally do not see this on search paths in /etc/resolv.conf files as the '.' at the end is used in a hostname specification.
If you /etc/resolv.conf had a search to include aaa.domain.com and bbb.domain.com when you request to resolve qqq, the resolver will try qqq, failing that try qqq.aaa.domain.com and then bbb.domain.com until either one succeeds or you have total failure.
In the same example if you put ddd.domain.com, the resolver would try ddd.domain.com, then try ddd.domain.com.aaa.domain.com and ddd.domain.com.bbb.domain.com in a similar manner.
If you put in ddd.domain.com. (note the final period), the resolver only searches ddd.domain.com ONLY and does not append anything from the /etc/resolv.conf search path.