Out of the very few times that Maupassant offers an insight of Monsieur Loisel's thoughts, a salient one is when the man is faced with the possibility of having to give to his wife a lot of money that he had saved up. He had just obtained an invitation to the Ministry of Education's ball, and Mathilde complained that she had nothing to wear; that she wanted a dress for the ball, and that she will have it for a few hundred francs.
Here is when we realize that the man had plans, after all, and a life of his own which he enjoys funding.
He grew a little pale, because he was laying aside just that amount to buy a gun and treat himself to a little shooting next summer on the plain of Nanterre, with several friends who went to shoot larks there of a Sunday.
While the extent of any other emotions of Monsieur is unknown, the best bet is to stick with this evidence that we do have and argue that this information helps us to see that Mathilde certainly has no other interests but those of her own. Moreover, we realize that Monsieur Loisel is not a bad husband, at all. He actually is willing to compromise for his wife. This is quite telling because we know that this is not mutual and, at the same time, sheds light as to who Mathilde really is.
Therefore, there is definitely a benefit to having some glimpses that show the feelings and emotions of Monsieur Loisel. His thoughts actually redeem him in the eyes of the reader and show his true character when juxtaposed to that of his wife.