There are many circumstances that can happen within your organisation which lead you to consider hiring a temp. In most circumstances, the need will be urgent and you should be able to have a qualified temp start with you immediately.
1) Employee leave cover
You may consider hiring a temp to cover holiday leave, sickness leave or maternity/paternity leave. It is understandable for you to think it is too time consuming to train a temp and we can cover amongst ourselves. It is great there is cross-functioning of roles within the team, however it would be good to understand the return on investment in hiring a temp to support with the less technical tasks, as you should expect them to be savvy in picking up a role quickly which leaves the full time employees to have full dedication to their actual role and not being stretched too thin. Stress and fatigue can leave employees carrying the extra workload more prone to sickness which leads to more employees taking time off, and less efficiency from your company as a whole.
2) Seasonal periods
Financial year ends, Christmas chaos, and general seasonal peaks and troughs within your business can be stressful and hard to manage with just full-time employees. By hiring temps to assist for a certain duration, you can alleviate yourself of the stress of busy periods without having to employ permanent staff.
3) Scoping a new role
Some businesses find it beneficial to hire a temp if they are in the process of scoping a newly created position within the organisation and are not quite sure how it looks yet. Temporary employees tend to have worked across an array of businesses and have acquired skills and ideas that they can bring to the role that are unbiased and an outside/fresh perspective.
Temporary employees are a great stand in for a role if there is no approval for the permanent headcount. Some candidates can temp in a role for many months (sometimes years!) and are essentially part of the furniture.
5) Fill in whilst you are recruiting permanently
Temps can assist in filling in whilst you go through the permanent recruitment process which can take some time. It is unlikely you will find an immediately available permanent employee, as most candidates in the permanent market are likely to have 4 - 6 week notice periods. In some instances, the temp can turn out to be the right permanent person.
If you do consider hiring a temp, your recruitment agent would want to have a thorough understanding of key details around the requirement so they can match the right temp to the right role accordingly. Be sure to be as clear and as detailed as possible to avoid the risk of not getting the right candidate and fit.