I just started writing a business plan, and I'm beginning to wonder if it's really necessary. Did all these blooming businesses around in Nigeria write business plans before they started. If you have a business plan for your business, what are the benefits?

The so called blooming businesses, some, may have not started out with s business plan but I can assure you that they had to as the business grew.
You need to have a business plan not as academic excersice but if you go through the process properly doing your reviews and replans in a dedicated way you'd be glad you did. It may not be a bad idea if you had an experienced mentor for guidance. Not to point you away from your passion but to polish you and your plans to lustre.

To add on.....what are the benefits you asked. You may simply look at it as a ship captain about to set sail. Your destination is defined, your crew, even the type of ship you'd start out with as the journey might be so long with boisterous winds you might need to dock at some points for supplies, a bigger ship more or new crew. What are the dos and donts for this trip. Your mission vission and core values had just been nailed. where are you? What are determinant factors that this ship would undertake a succesful voyage.....your SWOT analysis.
What are your budgets...your cashflows...your strategy/ tactics to deploy for this voyage/ business to succeed.

What are the business KPIs.....what factors are critical to the business success. What alternatives came up while developing your strategies...why did you settle with the ones you chose. By the time you go through this incubation/ business plan development process you'd be better prepared to set out than you ever thought.
Hope I was helpful.

kolokolobi: What are the business KPIs.....what factors are critical to the business success. What alternatives came up while developing your strategies...why did you settle with the ones you chose. By the time you go through this incubation/ business plan development process you'd be better prepared to set out than you ever thought.
Hope I was helpful.

Yes, this was helpful, thank you for your contribution. So do you have a business or a business plan?

Both.