is it important to use a ups if our electric connections are not good?

Answer 1

It is unlikely your computer will be damaged by a power outage. However, you will lose any unsaved work.

If you work with important documents, or if you're in the habit of waiting a long time between saves, buying a UPS might be a good investment.

Answer 2

Using an UPS is mostly dependent
on what you're using the computer for,
rather than power quality. But for
stuff like home PCs they make
what you could call a quasi-UPS (they're really
just save-and-power-down systems)
that are pretty inexpensive and are
a good investment for general purpose
desktop computers.