In Crusader Kings 2 with the Conclave DLC you can form your own mercenary band. As with most decisions there's a trade off: you gain income but your personal levies are reduced.
When have other players found it strategic to form their own mercenary bands? Is there a rule of thumb for how much to invest into the band?
For example, I'm currently playing as the Amalfi merchant republic. My demense is largely cities, so my personal levy is mostly light troops. Would it make sense therefore to form a mercenary band, reducing my levy of light troops, but increasing my income a little to give me the opportunity to hire other mercenary companies for heavy troops? But my income is over 1000 gold a year, so I assume I'd have to invest heavily for the income from the band to actually be a meaningful addition to my budget.