In an ordinary partnership, there is no limited liability: each partner is liable for the business debts of the partnership. This can help ensure that the partners are committed to the business - but equally, it can be personally disastrous if the business fails.
Separately, partners in a partnership pay income tax (and National Insurance contributions) on their share of the profits. Depending on how profitable the business is, and whether the partners want to reinvest in the business, this may be more or less tax-efficient than trading as a limited company.
In some cases, trading as a partnership is an attractive way for two or more people to form a business, particularly if the business risks are relatively low. But as the business grows, it is often a good idea to form a company: for increased flexibility, and to take advantage of limited liability. The main exception is in (the very few) businesses where you are required to trade as a partnership. In these cases, it is often advantageous to form a limited liability partnership
