If you're the only user on the machine it's okay, as long as you know what you're doing. The general concern is that by having your current directory in
PATH, you cannot see commands as a constant list. If you need to run a script/program from your current directory, you can always explicitly run it by prepending
./ to its name (you telling the system "I want to run this file from my current directory").
Say, now you have all these little scripts all over your filesystem; one day you'll run the wrong one for sure. So, having your
PATH as a predefined list of static paths is all about order and saving oneself from a potential problem.
However, if you're going to add
. to your
PATH, I suggest appending it to the end of the list (
export PATH=$PATH:.). At least you won't override system-wide binaries this way.
If you're a root on the system and have system exposed to other users' accounts, having
PATH is a huge security risk: you can
cd to some user's directory, and unintentionally run a malicious script there only because you mistyped a thing or script that has the same name as a system-wide binary.