You will want to clearly understand what the function Devote Place does especially after you have joined a guild.
As was explained on the page Underworld (Guild) Bosses there are two types of bosses that a guild can fight together: Encountered or Devote bosses. Under the Support tab you will mostly see Encountered Bosses....those that yourself or other guild members have randomly summoned at the end of a dungeon in which that boss is commonly seen.
Devote Bosses, however, need to be planned. They are a lot tougher to beat and if you are new to the game you will need a lot of help to kill one. Also, there will be gold as a reward at the end of the kill so it is best to understand just what your guild's approach to this type of Summons is.
How it WorksEdit
So, as you can see in the photo, each Devote Boss needs only 1 more item added (devoted) to reach it's limit .... ie: 19/20, 24/25. It is safe for you to devote your items up to this point.
However, when the limit is reached.... ie: 20/20, 25/25 that boss will then appear and the Devote Place page will be locked until the next day.... there is a cooldown period.
Good to KnowEdit
Now to take a look at the red circles in the first picture: Attack/Defense/Drop/EXP... these are directly related to the next guild tab: Guild Effect. So when making your decision on which boss is best to summons you may want to think about which effect (buff) will most benefit your guild. Yes, this buff is permanent and it will be applied to all members of the guild.
For example: this guild has reached the max (Lv 10 is allowable so far in the game) on all buffs except for EXP. Therefore only bosses such as Mizuchi, Three-eyed Priest, Night Grudge Serpent, and Heaven Roar would be of any value (see their pages under Participation rewards = Guild effect EXP)
Note* Also, if you are really working hard as a group to build the guild, you may want to frequent only those dungeons that have Encountered Bosses which give the buff you are seeking.
For the guild seeking only EXP they may want to run Forest of Wood God, Cave of Austere Priests, or Shrine of Black Smoke as encountering either Stone Lion, Chimpanzee, or Jade Rabbit (which reside there) will add a little bit. (see their pages under Participation rewards = Guild effect EXP)