When I’m about to play with other players, I like to check out their gear. I have often seen that some players are using only 2 weapon slots and no trinkets. I just assumed that they couldn’t afford the slots, but perhaps some people feel they are not worth it or don’t need them.
Now, while it’s true that I don’t always need them, I find the cost of 2 30-day trinket slots, 300 energy, and 2 30-day weapon slots, 500 energy, to be a very good value for my money when I consider the benefits they give me in terms of fun and strength. First of all, they make the game more fun because I can use a greater variety of weapons. Generally I have 2 swords and 2 guns, all of which I use, but for some levels such as Wolver’s Dens I like to bring along my Snarbolax bomb or a fire bomb in Aurora Isles levels or a freeze bomb for the Vanaduke fight. These are just personal preferences and not necessarily recommendations. Secondly, I mainly use heart trinkets because I enjoy having more health. I have survived countless battles with less than 10% health, and for me, not dying is certainly a more fun way to play the game. Occasionally I use Elite trinkets to make my weapons more effective.
While we certainly often don’t need weapon and trinket slots, I suppose there is an unspoken assumption that players will naturally want to makes themselves as strong as possible. They do this by finding the best combination of weapons and armor and supplementing these with trinkets and whatever unique variants they can find or afford. While we might intentionally limit ourselves for a fun challenge, a game that is too easy might get boring; however, I think there is plenty to challenge even the best players.
In summary, using 4 weapons and 2 trinkets makes me much stronger and also makes the game more fun, and I believe they are well worth the cost.
When I was playing this game at maximum intensity, I used three weapon slots. I was generating crowns quickly enough that I could easily afford one trinket slot upgrade per month, but I found that two upgrades was more than needed (diminishing returns).
More recently, I've used weapon slot upgrades "tactically". For example, if I know that I'm going to play a lot in a given month, including a couple of Shadow Lair runs, then I might activate one.
Disappointingly, my weapon diversity has declined with my use of weapon slot upgrades. When I equip only two weapons, I have less flexibility in practicing quirky, weak weapons.
My use of trinket slot upgrades has plummeted with my accumulation of UVs and Black Kat armor.