Near the start of a legal career, this decision is less important for lawyers whose practice has developed among and with other lawyers. Typically such lawyers stay in their “family” neighborhood at least until they have solidified their client relations. Still, there are basic questions about partnership that rainmakers at all stages of their careers need to consider.
There are two categories of choices rainmakers face concerning partnerships: the threshold one of “whether” one wants to be a partner with others and then, if one does want a partner, “who” you want as a partner. (Non-rainmakers, like most employees, have more limited choices.)
Having a partner is not essential to success. Nor is it something all well-adjusted professionals should necessarily want. Do you need or want a peer decision maker to help plan your work and manage client relationships? Do your clients regularly need work in areas you cannot handle? Even when these things are true, there are tactical, financial and technical reasons to be happy with a non-committed professional relationship. However, when law partnerships are good, they can be very, very good. Synergy happens within well matched law partnerships, regarding both finances and professional development. How responsibilities and profits are shared is a separate decision, and varies enormously among law partners.
There are also basic considerations concerning who should be your partner(s). Billing rates are crucial. Well functioning partnerships want to encourage clients to stay for all possible services. Shelled peanuts followed by truffles make clients balk. Synergistic or overlapping practices are important for the same reasons. Clients need legal work in related fields, not distant ones.
Working styles, regarding attitude and energy, matter. I have seen lawyers who work well in crisis scream at partners who freeze when bad things happen in deals or litigations. Likewise, deliberative types cringe at decisions being made without all available facts being considered.
It matters if you care about your partners. You may march off into the sunset with them. However, as always, with common values, concern and affection can grow over time. At the start, you should trust your partners. Affection is a bonus.