I think 538's reasons are all good:

Why we’re tracking endorsements

• • Party elites use endorsements to influence not only voters but also each other, hoping to get other powerful party members to rally behind the candidate they think would be most acceptable.
• • The pace of endorsements — whether leaders coalesce early around a single candidate or are backing a variety of candidates — can indicate how drawn out the primary season will be.
• • A lack of a consensus can mean that party leaders’ first-choice candidate may have more trouble securing the nomination.
• Also, seeing them made me realize that in normal times--that is, when we don't have a severe nut case for president who as part of his sanity problem is that he isn't loyal to anyone but himself and draws all the air out of the country and turns traditional party ideology upside down, etc.--these intraparty relationships tell you a lot more about power in the government among those who actually hold it, and they are not the president. Traditionally, the most important thing the president does, where he/she only matters: federal court appointments; foreign policy. And it would be less of the latter if Congress did what it was supposed to do on interventions. The president doesn't run this country as far as what matters to most people's lives, period. The presidential race, it's a kabuki show. Who your Congressional reps. are and what party controls Congress is far far more important.