Yes, I also avoid betting on matches that don't require them to win, one of which is a pre-season match for example, even if the match brings together two very different clubs. In fact, I personally avoid betting on competitions that are less prestigious or in other words are not a top priority for the club.
Testing strategies in a friendly match is more useful in my opinion than looking at the final score of the match. In fact, some coaches don't set any targets before the match starts and only focus on what they can do in the match. It's not uncommon for them to field players who don't have many opportunities in competitions to see their abilities in an experiment that the coach carries out.
Matches like this are usually better just watching than gambling on such games because like you did said they don't really have to win such games probably because they know they don't have anything to lose if they lose such games because it's just a friendly game just to get prepared for the league.
Usually such games are used to test strategies and probably check the team strength and improve on their strategies which they will be using through the season, sometimes they don't use their star players because they don't want them to probably get injured of fatigued so they mostly use rotational players so as to test their abilities and see if they can fit in matches during the season should Incase the need arise due to injuries or red cards where some players may have to miss some matches, so basically friendlies and preseason are used to test team strength and strategies in most cases.