OK. Even in the remotest parts of North Wales you will not encounter any mono-lingual Welsh speakers (even though it may initally appear that this is the case).
You don't need Welsh as a tourist to buy food, visit the supermarket and go to the pub.
You don't need Welsh to ask for directions to your hotel in Cardiff.
But it is one of the national languages of the United Kingdom.
Learning a few phrases is doing your (tiny) bit to help the language survice.
And also by learning Welsh ...
... you are striking a blow against the entrenched power structures that have marginalised and discouraged languages other than English over the centuries.
Call me cynical, but these power structures probably don't have your best interests at heart either but exist to protect the establishment and massively wealty elite ...
... so, learn a few Welsh words and make the world a better place.
So that was slightly tongue in cheek but ...;)
See also Basic Words. 2.