There seems to be chatter among industry experts regarding whether liking a Google review has any influence in Google's decision to highlight it or not. It seems that reviews that've received at least one like are about 5x as likely to become a highlighted review when compared against those without one.
As of August 2019, likes are a fairly unregulated sector in GMB, as there doesn't seem to be a set of guidelines or policy in place. Unlike reviews, where reviewing your own business is in direct violation of Google's policy, there doesn't seem to be any recourse for a business liking reviews left on any of their location pages.
Due to there seeming to be some potential gain here, we have a couple recommendations for utilizing the review likes function;
Like intentionally - When you receive a review you genuinely appreciate, go ahead and give it a thumbs up; That simple action could have some influence on what makes it to the front of your listings.
Don't spam - Resist the temptation to go and like every positive review as majority of Google reps would consider that to be spam. The repercussions this could bring to your listings are not worth the headache.
Keep it civil - On a similar note, also refrain from purposely liking your competitors' negative reviews in hopes to move them to the front of their listing.
How important is it to take advantage of this feature?
This probably won't be what makes or breaks your listing, and as such, shouldn't be what makes it to the top of your priority list. If reputation management is a primary focus for your brand, there's plenty more advantageous items to devote your time and energy into.
Due to the lack of exploration on the matter, it's hard to know what material benefit can be gained from liking certain types of reviews - However, based on what has been investigated, there remains the implication that by liking reviews, you can then increase the probability of that review getting highlighted.
Ultimately, despite the lack of substantial research, this is still something to consider doing on occasion.