Being spontaneous and deciding not to plan is a great idea SOMETIMES, but not all the time. Especially if you plan to travel overseas, you might need to take a step ahead and plan everything out. Here are some drawbacks of refraining from making the mandatory vacation preparations;

Spending issues
Budgeting is a big issue when considering spending it on a vacation. If it is not planned prior to the trip, it can end up costing way more than you expect it to. There are many things that need planning and allocating while on vacation, like accommodation, transport, food, entertainment, shopping and emergencies. Proper planning can eliminate all of the problems that can be caused regarding money.
Time
By booking tours like the Finland northern lights tour, night safari tours or anything of that sort beforehand, you are benefitted with the opportunity to experience the main attractions in the country without fail. And by methodically planning it out, you are able to manage time adequately to engage in whatever you want to do.
Tourist traps
Without proper planning and research, a sloppy tour guide might take you to places that seem useless and cost a fortune too. Therefore, as stated previously it is better to make prior bookings and do necessary research on what you want to visit.
The stress
If you are a person who is not very accustomed to spontaneous trips, then chances are that you are bound to be really stressed all throughout the trip due to the absence of a plan in your mind. Avoid stress and agitation by planning ahead of the trip.
Transportation
Transport is one of the things that cost the most during a vacation. Booking a hotel closest to your point of attraction would limit the cost incurred and be effective for the pocket as well. There will also be no need to bargain for cheap rides around town.

Not getting the most out of it
By planning early and making necessary arrangements to visit the tourist attractions, you are able to get the most out of the vacation, instead of reaching home and realizing how close you were to have visited many places but missed out because of the lack of planning.
Given above are the downsides of a spontaneous trip, but that does not mean it will not be good, but it is not a guarantee for the cost you intend on spending. By following corrective measures to plan and organize a trip, your safety and enjoyment can be assured.