Always recommend a surge protector.
.. They do nothing for Brown outs, Low voltage
.. No protection from Loss of power
.. No protection for "low energy" spikes
So what does the Surge protector really do.
.. Protects against High energy spikes. For example a Near By (Not a direct hit) by lighting can create a Large energy spike.
.. When The AC drops to zero momentarily then comes right back on, some appliancies can generate a large spike which may trigger The protection circuit - often it is not high enough.
NOTE: The protection circuit is normally a self destruct circuit which means if you trigger it you will need to replace the surge protector.
Above reasons are why you should have a UPS + Surge protector (Most UPS have a built in surge protector).
Bottom Line when you can afford the UPS - Get it. It is cheaper than replacing the computer.
My Aunt had a lighting strike. She had a surge protector - NO help she still lost the computer. Reason the Spike also came in on the phone line and she had a mode connected.